Ziegler-Natta catalyst systems are well known for their capability to polymerize olefins. They in general consist of a support which mostly is magnesium based onto which titanium component has been added along with organic compound known as internal donor. This catalyst when combined with co-catalyst and/or external donor comprise of the complete ZN catalyst system.
Ziegler-Natta catalyst system typically consists of transition metal halide normally titanium halide supported on metal compound which is typically magnesium dichloride. Along with transition metal, there is an organic component known as internal electron donor that plays a typical role during catalyst synthesis and polymerization. MgCl2 carrier, where the MgCl2 is in active form, can be created by various methodologies. One of the methods is precipitating the MgCl2 from an organic solution where magnesium is present as a soluble compound. The soluble magnesium compound can be achieved by starting from a magnesium alkyl and treating it with an alcohol. This step is then followed by chlorination of Mg alkyl or alkoxy compounds by a chlorination agent. The magnesium carrier can also be precipitated in the form of ‘ready-made’ MgCl2. In that case the MgCl2 has to be dissolved first in some suitable donor compound and then precipitated in hydrocarbon solvent. The MgCl2 support material can also be precipitated by chlorinating a soluble magnesium alkyl compound simply by treating it with chlorine gas or hydrochloric acid. Once the desired specification of carrier is obtained, this is generally followed by titanation procedure which finally results in the catalyst synthesis.
U.S. Pat. No. 4,220,554 of Montedison describes the process of synthesizing the catalyst by treating Ti compounds with a spherical carrier which consists of Mg compound having the formula XnMg(OR)2-n. XnMg(OR)2-n is synthesized by in reacting, in a single step, Mg metal, the organic halide and the orthosilicic acid ester. This product is isolated and then treated with halide of aromatic acid which is again isolated and treated with Ti compound for formation of catalyst. This catalyst is evaluated for propylene polymerization. This route applies the usage of orthosilicic ester for generation of magnesium alkoxy halide compound and focuses on the particle shape as well as size of the catalyst.
U.S. Pat. No. 4,727,051 of Stauffer Chemical Company discloses the process for synthesis of XnMg(OR)2-n by preparing an alkanol adduct of a magnesium halide, reacting the product of this step with metallic magnesium, and drying the product. The compositions are then evaluated for as catalysts of olefin polymerization. The main disadvantage of this process is the usage of magnesium halides and large amount of alcohols.
U.S. Pat. No. 4,820,672 of Lithium Corporation of America describes the process for producing magnesium halide alcohol complex by reacting in an ether free hydrocarbon reaction medium, magnesium metal, dialkyl magnesium, alkyl magnesium halide, alkyl magnesium alkoxide, magnesium dialkoxide and alkoxy magnesium halide with an anhydrous hydrogen halide in the presence of chlorosubstituted alcohol. Further this complex is used for synthesis of ZN catalyst. The main disadvantage of this process is a large number of steps are involved for magnesium halide alcohol synthesis and further the usage of hydrogen halide which is difficult to handle. U.S. Pat. No. 4,820,879 further describes the process where alkoxy magnesium halides are formed by reacting preactivated magnesium with alcohol at higher temperatures and then treating it with hydrogen halides. Here also usage and handling of hydrogen halide is quite troublesome.
U.S. Pat. No. 4,792,640 discloses a process for synthesis of solid hydrocarbyloxymagnesium halides which is ether free, where preactivated (with iodine) magnesium metal is reacted with alkyl halide for some time and then addition of alcohol is done dropwise and finally refluxed. The solid product is filtered, dried and analyzed. Here the Grignard is stabilized in hydrocarbon. These patents contains no information on the activity of the ZN catalyst synthesized thereof.
U.S. Pat. No. 5,081,320 of Akzo NV describes the synthesis of alkoxymagnesium halides from secondary alcohol containing alkyl branching on the alpha carbon atom which is soluble in inert hydrocarbon. The process involves heating inert hydrocarbon solvent, secondary alcohol and ethanol with magnesium halide (MgCl2) to dissolve the magnesium halide. Magnesium metal is then added along with additional solvent to prepare a soluble alkoxymagnesium halide. One disadvantage of this process is one need to prepare soluble magnesium alkoxide in order to further react the magnesium metal. U.S. Pat. No. 5,108,972 discloses the process of synthesis of alkoxymagnesium halide using non Grignard route where they react magnesium halide and magnesium alkoxide in excess of alcohol. Further magnesium source can also be added which is generated through dialkylmagnesium in hydrocarbon. Main disadvantage of this process is usage of expensive raw materials and large number of steps. The patent describes the process of synthesizing the magnesium compounds only.
U.S. Pat. No. 5,414,158 of Witco GmbH describes the one step synthesis of alkoxymagnesium halides in an inert hydrocarbon by reacting preactivated magnesium with small quantities of magnesium alkyl, with almost equimolar mixture of an alkyl halide and an alkanol. The obtained product is in excess of 90%. In this process first magnesium needs to be activated with magnesium alkyl at high temperature and then addition is carried out dropwise to the alkylhalide and alkanol mixture. One disadvantage of this process is requirement of expensive magnesium alkyl for activation which is also difficult to handle and further the extra addition of alkanol after the reaction to reduce viscosity. This patent describes the synthesis of alkoxymagnesium halide only and doesn't state the usage of the same as precursor for ZN catalyst.
EP1273595 of Borealis describes the process for synthesis of catalyst by reacting dialkylmagnesium with monohydric alcohol followed by dicarboxylic acid dihalide and chlorinated hydrocarbons. After washing and isolation of this product, it is further treated with titanium compound for the formation of ZN catalyst which shows activity for propylene polymerization. The main disadvantage of this process is usage of expensive dialkylmagnesium and its handling. This patent is mainly on the usage of emulsion stabilizer for controlling the particle size and shape.
U.S. Pat. No. 7,135,531 of BASF discloses the process for the synthesis of spherical catalyst which essentially contains titanium, internal donor and a support made from a magnesium compound, an alcohol, ether, a surfactant, and an alkyl silicate. The magnesium compound mainly magnesium dichloride is dissolve in alcohol at higher temperature and then treated with ether at lower temperature followed by addition of emulsifier at still lower temperature. This is then treated with silicate and titanium compound and final catalyst is ready after washing and drying. The main disadvantage of this process is higher alcohol content and expensive raw materials.
US2009/0306315 of SABIC discloses the process for preparing a polymerization catalyst which is synthesized by reacting Mg(OR1)xCl2-x, which is obtained by reacting a Grignard compound with an alkoxy or aryloxy silane compound, with electron donor in the presence of inert dispersant to give an intermediate reaction product which is then treated with titanium halide to give the final catalyst which shows activity for olefin polymerization. This process has main disadvantage that its involves large number of steps which mainly consists of first solubilizing the magnesium compound and then solidifying before making final catalyst.
Thus, it would be desirable to provide a solid organometallic precursor compound for synthesis of a catalyst for polymerization of olefins that could be synthesized through a single step process using less expensive raw materials and lower alcohol content. Further, it would be desirable if the organometallic compound could be isolated, without any further purification and used as a precursor for making olefin polymerization catalyst which is highly active with low xylene solubility and excellent hydrogen response.